U.S. patent application number 11/823815 was filed with the patent office on 2009-01-01 for thermal management in imaging reader.
Invention is credited to Edward Barkan, Bradley Carlson, Mark Drzymala.
Application Number | 20090001174 11/823815 |
Document ID | / |
Family ID | 39794762 |
Filed Date | 2009-01-01 |
United States Patent
Application |
20090001174 |
Kind Code |
A1 |
Barkan; Edward ; et
al. |
January 1, 2009 |
Thermal management in imaging reader
Abstract
A reader for electro-optically reading indicia, includes a
solid-state imager including an array of image sensors for
capturing return light from the indicia during reading, and a light
source for generating and directing high intensity illumination
light to the indicia with concomitant generation of excess heat.
Thermal management procedures for dissipating the excess heat are
performed to improve reader performance.
Inventors: |
Barkan; Edward; (Miller
Place, NY) ; Drzymala; Mark; (Commack, NY) ;
Carlson; Bradley; (Huntington, NY) |
Correspondence
Address: |
KIRSCHSTEIN, OTTINGER, ISRAEL;& SCHIFFMILLER, P.C.
425 FIFTH AVENUE, 5TH FLOOR
NEW YORK
NY
10016-2223
US
|
Family ID: |
39794762 |
Appl. No.: |
11/823815 |
Filed: |
June 28, 2007 |
Current U.S.
Class: |
235/462.42 |
Current CPC
Class: |
G06K 7/10732 20130101;
G06K 7/10584 20130101; G06K 7/10544 20130101 |
Class at
Publication: |
235/462.42 |
International
Class: |
G06K 7/10 20060101
G06K007/10 |
Claims
1. A reader for electro-optically reading indicia, comprising: a
solid-state imager including an array of image sensors for
capturing return light from the indicia during reading; a light
source for generating and directing high intensity illumination
light to the indicia with concomitant generation of excess heat;
and a heat dissipater for dissipating the excess heat to improve
reader performance.
2. The reader of claim 1, and a controller for energizing the light
source with a high amplitude drive current to generate the high
intensity illumination light during the reading.
3. The reader of claim 1, and a housing having a presentation area,
and wherein the light source is located within the housing and
directs the high intensity illumination light through the
presentation area to the indicia for reflection therefrom as the
return light.
4. The reader of claim 1, wherein the heat dissipater is operative
for conducting the excess heat away from the light source.
5. The reader of claim 1, wherein the heat dissipater includes a
printed circuit board having opposite surfaces; wherein the light
source includes a light emitting diode (LED) surface-mounted on one
of the surfaces of the board; and wherein the heat dissipater
further includes thermally conductive lands on the opposite
surfaces of the board, and a hole extending through the opposite
surfaces of the board and being plated with a thermally conductive
layer in thermal communication with the lands, and wherein the LED
is in thermal communication with one of the lands to conduct the
excess heat away from the LED.
6. The reader of claim 5, and a chassis comprised of a thermally
conductive material, for supporting the imager and the light
source, and being in thermal communication with one of the lands to
conduct the excess heat away from the LED to the chassis.
7. The reader of claim 1, wherein the heat dissipater includes a
thermal sensor located in a circumambient region of the light
source, for sensing when the excess heat reaches a predetermined
threshold, and for generating a control signal when the threshold
has been reached.
8. The reader of claim 7, and a controller operatively connected to
the light source and the thermal sensor, for causing the excess
heat to be reduced upon generation of the control signal.
9. The reader of claim 8, and a host operatively connected to the
light source and the thermal sensor, for causing the excess heat to
be reduced upon generation of the control signal.
10. The reader of claim 9, wherein at least one of the controller
and the host is operative for shutting off the light source upon
generation of the control signal.
11. The reader of claim 9, wherein at least one of the controller
and the host is operative for energizing the light source for a
time period during reading with the high intensity illumination
light, and is further operative for shortening the time period upon
generation of the control signal.
12. The reader of claim 9, wherein at least one of the controller
and the host is operative for driving the light source with a high
amplitude drive current during reading with the high intensity
illumination light, and is further operative for reducing the high
amplitude drive current upon generation of the control signal.
13. The reader of claim 9, wherein at least one of the controller
and the host is operative for driving the light source comprised of
a plurality of light emitting diodes (LEDs) during reading with the
high intensity illumination light, and is further operative for
reducing the number of LEDs upon generation of the control
signal.
14. The reader of claim 9, wherein at least one of the controller
and the host is operatively connected to the imager, and is
operative for causing the imager to capture the return light in a
plurality of images per frame during reading with the high
intensity illumination light, and is further operative for reducing
the number of images captured per frame upon generation of the
control signal.
15. The reader of claim 9, wherein at least one of the controller
and the host periodically energizes the light source to cause the
high level illumination light to illuminate the indicia during a
plurality of frames, and periodically deenergizes the light source
to cause the high level illumination light not to illuminate the
indicia during at least one of the frames upon generation of the
control signal.
16. The reader of claim 7, and a chassis for supporting the imager
and the light source in an imaging module, and wherein the thermal
sensor is supported by, and is in thermal communication with, the
chassis.
17. The reader of claim 1, wherein the light source is operative
for directing the high intensity illumination light in an aiming
pattern to and on the indicia.
18. A reader for electro-optically reading indicia, comprising:
imager means for capturing return light from the indicia during
reading; means for generating and directing high intensity
illumination light to the indicia with concomitant generation of
excess heat; and means for dissipating the excess heat to improve
reader performance.
19. A method of electro-optically reading indicia, comprising the
steps of: capturing return light from the indicia during reading by
using a solid-state imager including an array of image sensors;
generating and directing high intensity illumination light from a
light source to the indicia with concomitant generation of excess
heat; and dissipating the excess heat to improve reader
performance.
20. The method of claim 19, and energizing the light source with a
high amplitude drive current to generate the high intensity
illumination light during the reading.
21. The method of claim 19, and configuring a housing with a
presentation area, and locating the light source within the
housing, and directing the high intensity illumination light
through the presentation area to the indicia for reflection
therefrom as the return light.
22. The method of claim 19, wherein the dissipating step is
performed by conducting the excess heat away from the light
source.
23. The method of claim 19, and surface-mounting a light source
comprised of a light emitting diode (LED) on one of a pair of
opposite surfaces of a printed circuit board; and wherein the
dissipating step is performed by providing thermally conductive
lands on the opposite surfaces of the board, and plating a hole
extending through the opposite surfaces of the board with a
thermally conductive layer in thermal communication with the lands,
and providing thermal communication between the LED and one of the
lands to conduct the excess heat away from the LED.
24. The method of claim 23, and supporting the imager and the light
source by a chassis comprised of a thermally conductive material,
and providing thermal communication between the chassis and one of
the lands to conduct the excess heat away from the LED to the
chassis.
25. The method of claim 19, wherein the dissipating step is
performed by locating a thermal sensor in a circumambient region of
the light source, sensing when the excess heat reaches a
predetermined threshold, and generating a control signal when the
threshold has been reached.
26. The method of claim 25, and causing the excess heat to be
reduced upon generation of the control signal.
27. The method of claim 25, and shutting off the light source upon
generation of the control signal.
28. The method of claim 25, and energizing the light source for a
time period during reading with the high intensity illumination
light, and shortening the time period upon generation of the
control signal.
29. The method of claim 25, and driving the light source with a
high amplitude drive current during reading with the high intensity
illumination light, and reducing the high amplitude drive current
upon generation of the control signal.
30. The method of claim 25, and driving the light source comprised
of a plurality of light emitting diodes (LEDs) during reading with
the high intensity illumination light, and reducing the number of
LEDs upon generation of the control signal.
31. The method of claim 25, and causing the imager to capture the
return light in a plurality of images per frame during reading with
the high intensity illumination light, and reducing the number of
images captured per frame upon generation of the control
signal.
32. The method of claim 25, and periodically energizing the light
source to cause the high level illumination light to illuminate the
indicia during a plurality of frames, and periodically deenergizing
the light source to cause the high level illumination light not to
illuminate the indicia during at least one of the frames upon
generation of the control signal.
33. The method of claim 25, and supporting the imager and the light
source in a chassis of an imaging module, and supporting the
thermal sensor by, and in thermal communication with, the
chassis.
34. The method of claim 19, wherein the directing step is performed
by directing the high intensity illumination light in an aiming
pattern to and on the indicia.
35. An imaging module for use in electro-optically reading indicia,
comprising: a chassis; a solid-state imager supported by the
chassis, including an array of image sensors for capturing return
light from the indicia during reading; a light source supported by
the chassis, for generating and directing high intensity
illumination light to the indicia with concomitant generation of
excess heat; and a heat dissipater for dissipating the excess heat
to improve reading performance.
36. The module of claim 35, wherein the heat dissipater includes a
printed circuit board supported by the chassis and having opposite
surfaces; wherein the light source includes a light emitting diode
(LED) surface-mounted on one of the surfaces of the board; and
wherein the heat dissipater further includes thermally conductive
lands on the opposite surfaces of the board, and a hole extending
through the opposite surfaces of the board and being plated with a
thermally conductive layer in thermal communication with the lands,
and wherein the LED is in thermal communication with one of the
lands to conduct the excess heat away from the LED.
37. The module of claim 35, wherein the chassis is comprised of a
thermally conductive material, and is in thermal communication with
one of the lands to conduct the excess heat away from the LED to
the chassis.
38. The module of claim 35, wherein the heat dissipater includes a
thermal sensor supported by the chassis in a circumambient region
of the light source, for sensing when the excess heat reaches a
predetermined threshold, and for generating a control signal when
the threshold has been reached.
39. The module of claim 35, wherein the light source is operative
for directing the high intensity illumination light in an aiming
pattern to and on the indicia.
Description
DESCRIPTION OF THE RELATED ART
[0001] Flat bed laser readers, also known as horizontal slot
scanners, have been used to electro-optically read one-dimensional
bar code symbols, particularly of the Universal Product Code (UPC)
type, at a point-of-transaction workstation in supermarkets,
warehouse clubs, department stores, and other kinds of retailers
for many years. As exemplified by U.S. Pat. No. 5,059,779; No.
5,124,539 and No. 5,200,599, a single, generally horizontal window
is set flush with, and built into, a generally horizontal
countertop of the workstation. Products to be purchased bear an
identifying symbol and are typically slid or swiped across the
generally horizontal window through which a multitude of scan lines
in a scan pattern is projected in a generally upward direction.
Each scan line is generated by sweeping a laser beam from a laser.
When at least one of the scan lines sweeps over a symbol associated
with a product, the symbol is processed and read, and the product
is identified.
[0002] Instead of, or in addition to, a horizontal slot scanner, it
is known to provide a vertical slot scanner, which is typically a
portable reader placed on the countertop such that its window is
generally vertical and faces an operator at the workstation. The
generally vertical window is oriented generally perpendicularly to
the horizontal window, or is slightly rearwardly inclined. A scan
pattern generator within the vertical slot scanner also sweeps a
laser beam and projects a multitude of scan lines in a scan pattern
in a generally outward direction through the generally vertical
window toward the operator. The operator slides or swipes the
products past either window from right to left, or from left to
right, in a "swipe" mode. Alternatively, the operator merely
presents the symbol on the product to the center of either window
in a "presentation" mode. The choice depends on operator preference
or on the layout of the workstation.
[0003] These point-of-transaction workstations have been long used
for processing transactions involving products associated with
one-dimensional symbols each having a row of bars and spaces spaced
apart along one direction, and for processing two-dimensional
symbols, such as Code 39, as well. Code 39 introduced the concept
of vertically stacking a plurality of rows of bar and space
patterns in a single symbol. The structure of Code 39 is described
in U.S. Pat. No. 4,794,239. Another two-dimensional code structure
for increasing the amount of data that can be represented or stored
on a given amount of surface area is known as PDF417 and is
described in U.S. Pat. No. 5,304,786.
[0004] Both one- and two-dimensional symbols can also be read by
employing solid-state imagers to capture an image of each symbol,
instead of moving a laser beam across each symbol in a scan
pattern. For example, the imager may comprise a one- or
two-dimensional array of cells or photosensors, which correspond to
image elements or pixels in a field of view of the imager. Such an
array may be comprised of a one- or two-dimensional charge coupled
device (CCD) or a complementary metal oxide semiconductor (CMOS)
device, analogous to those devices used in a digital camera to
capture images. The imager further includes electronic circuitry
for producing electrical signals indicative of the light captured
by the array, and a microprocessor for processing the electrical
signals to produce each captured image.
[0005] It is therefore known to use a solid-state imager for
capturing a monochrome image of a symbol as, for example, disclosed
in U.S. Pat. No. 5,703,349. It is also known to use a solid-state
imager with multiple buried channels for capturing a full color
image of a target as, for example, disclosed in U.S. Pat. No.
4,613,895. It is common to provide a two-dimensional CCD with a
640.times.480 resolution commonly found in VGA monitors, although
other resolution sizes are possible.
[0006] It is also known to energize an illuminator associated with
the imager-based reader to illuminate the symbol during its reading
with illumination light emitted from an illumination light source
and directed to the symbol for reflection therefrom. The
illumination light source is preferably at least one light emitting
diode (LED), and may include a plurality of LEDs. The illumination
light source and the imager are typically mounted on a chassis to
constitute an imaging engine or module that is located within the
reader.
[0007] The reading performance of imager-based or imaging readers
is highly dependent on the level of the illumination light that is
directed to the symbol. If higher levels of the illumination light
are to be projected from the imaging module for better reading
performance, it will be necessary to drive the illumination LEDs
that are mounted on the module at relatively high electrical drive
currents, thereby concomitantly causing significant heat
generation.
[0008] Although the known imaging readers are generally
satisfactory for their intended purpose, this heat generation can
cause significant problems, especially when the module is operating
in a hot environment, and/or when installed in a housing that does
not allow for heat dissipation. Excessive heat can reduce the
operating lifetimes of the LEDs and other reader components, and
can also degrade the performance of the imager itself. Some modules
use a laser or LED aiming pattern generator to project an aiming
pattern or mark on the symbol, which can also generate undesirable,
and be damaged by, excessive heat, as well as degrading other
components within the reader.
SUMMARY OF THE INVENTION
[0009] One feature of the present invention resides, briefly
stated, in an imaging reader for, and a method of,
electro-optically reading indicia, especially one- and/or
two-dimensional symbols. Each symbol includes elements of different
light reflectivity, i.e., bars and spaces. The reader could be
configured as a hands-free and/or a hand-held housing having a
window. The housing may have a handle for hand-held operation
and/or a base for supporting the housing on a support surface for
hands-free operation.
[0010] In some applications, the window could be omitted, in which
event, the reader has a windowless opening at which the indicia are
located for reading. As used herein, the term "presentation area"
is intended to cover both a window and a windowless opening. In the
case of the hands-free reader, the symbol is swiped past, or
presented to, the presentation area and, in the case of the
hand-held reader, the reader itself is moved and the presentation
area is aimed at the symbol. In the preferred embodiments, the
reader is installed in a retail establishment, such as a
supermarket, especially in a cramped environment.
[0011] A one- or two-dimensional, solid-state imager is mounted in
the imaging reader, and includes an array of image sensors
operative for capturing return light from a one- or two-dimensional
symbol or target through the presentation area during the reading
to produce a captured image. Preferably, the array is a CCD or a
CMOS array.
[0012] When the imaging reader is operated in low light or dark
ambient environments, a light source is provided, typically inside
the reader, for generating and directing illumination light through
the presentation area to the indicia to illuminate the symbol. The
light source preferably comprises one or more illumination light
emitting diodes (LEDs). To facilitate reading, many readers are
equipped with another light source, typically an aiming LED or a
laser, operative for directing illumination light in a visual
aiming pattern to and on the indicia. A controller or programmed
microprocessor is operatively connected to the imager and the light
source for controlling their operation.
[0013] As discussed above, the reading performance of the imaging
reader is highly dependent on the level of the illumination light
that is directed to the symbol. The higher the level of the
illumination light, the better is the reading performance. Hence,
high-powered light source(s) are electrically driven at relatively
high electrical drive currents, thereby projecting high intensity
illumination light onto the symbol. This, however, concomitantly
undesirably generates significant excess heat that can degrade and
shorten the working lifetime of components of the reader,
especially the imager, the light source(s) and the controller.
[0014] In accordance with one aspect of the invention, various
thermal management procedures are employed to dissipate the excess
heat to improve reader performance. For example, each illumination
LED is surface-mounted on one of a pair of opposite surfaces of a
printed circuit board. Thermally conductive, metallized lands or
pads, preferably of copper, are plated on the opposite surfaces of
the board. A hole extends through the opposite surfaces of the
board and is internally plated and lined with a thermally
conductive, metallized layer, preferably of copper, in thermal
communication with the lands on the opposite surfaces of the board.
The LED is in thermal communication, preferably by soldering, with
one of the lands to conduct the excess heat away from the LED from
one of the lands on one surface via the plated hole to the lands on
the opposite surface. This thermal management procedure is
especially recommended when the board is small in area such that
the lands on one surface, i.e., the front surface, of the board are
insufficient in area to radiate the excess heat to the environment.
By also using the land on the opposite rear surface to dissipate
the excess heat, the total area for radiating the excess heat to
the environment is increased, and the heat-sinking capability is
enhanced.
[0015] A chassis comprised of a thermally conductive material,
e.g., zinc, is operative for supporting at least the imager and the
high-powered light source(s) to constitute an imaging module or
scan engine. The chassis is preferably in thermal communication
with one of the lands to conduct the excess heat away from the LED
to the chassis. The opposite rear surface of the board is in close
proximity with the thermally conductive chassis of the scan engine.
Provision is made to conduct the excess heat from the opposite rear
surface of the board to the chassis by means of a heat conductive
medium, such as thermal grease or thermally conductive, silicone
pads. Alternatively, the lands on the opposite rear surface of the
board can be positioned in direct contact with the chassis. As a
result, the entire chassis now becomes part of the heat sink for
the high-powered light source(s).
[0016] It is known in prior art imaging engines to constitute the
chassis of a thermally insulating material, such as plastic.
However, the plastic chassis added no heat sinking ability. It is
also known in prior art imaging engines to constitute the chassis
of a thermally conductive material, such as metal. However, a
leaded, not surface-mounted, LED was used and, hence, no provision
existed to transfer heat from the LED to the chassis.
[0017] The metal chassis can have ribs or fins to aid in radiation
of the excess heat to the ambient environment, but sometimes the
scan engine is embedded in a product in such a way as to make
radiation of the excess heat unavailable. Worse yet, the scan
engine may be mounted close to a heat source that may actually
increase the temperature of the scan engine. In these cases,
additional measures must be taken to assure that the LEDs, and
other electronic components in the engine, do not overheat.
[0018] In accordance with another aspect of this invention, a
thermistor, a thermocouple, or a like thermal sensor is located in
a circumambient region of the light source, for monitoring the
temperature of the chassis and sensing when the excess heat reaches
a predetermined threshold, and for generating a control signal when
the threshold has been reached. For example, the thermal sensor can
be mounted on a circuit board close to, or in contact with, the
chassis. Thermal grease or other thermally conductive material may
be used to insure that the thermal sensor is thermally connected to
the chassis, the circuit board that supports the LEDs, or other
part of the scan engine that is deemed to be representative of the
temperature sensitive components in the scan engine that must be
protected from overheating. The controller is advantageously
operative for causing the excess heat to be reduced upon generation
of the control signal. Alternatively, or in addition, a host in
communication with the reader is provided for causing the excess
heat to be reduced upon generation of the control signal.
[0019] Various thermal management procedures include at least one
of the controller and the host being operative for shutting off the
light source upon generation of the control signal; or for
energizing the light source for a time period during reading with
the high intensity illumination light, and for shortening the time
period upon generation of the control signal; or for driving the
light source with a high amplitude drive current during reading
with the high intensity illumination light, and for reducing the
high amplitude drive current upon generation of the control signal;
or for driving the light source comprised of a plurality of light
emitting diodes (LEDs) during reading with the high intensity
illumination light, and for reducing the number of LEDs upon
generation of the control signal; or for causing the imager to
capture the return light in a plurality of images per frame during
reading with the high intensity illumination light, and for
reducing the number of images captured per frame upon generation of
the control signal; or for periodically energizing the light source
to cause the high level illumination light to illuminate the
indicia during a plurality of frames, and periodically deenergizing
the light source to cause the high level illumination light not to
illuminate the indicia during at least one of the frames upon
generation of the control signal. All of these thermal management
procedures have in common the feature of reducing the heat
generated by the LEDs. The thermal management procedures may be
initiated in succession or in combinations depending on how hot the
scan engine gets. At a first temperature threshold, moderate
thermal management procedures can be initiated. If temperature
continues to rise, further more aggressive thermal management
procedures can be initiated.
[0020] One possible thermal management procedure could be to
inhibit activation of the LEDs and other components of the engine
entirely until such time as the temperature returns to an
acceptable threshold level. Another possibility is to reduce the
time that the LEDs are permitted to be turned on for each exposure
of the imager. Other possibilities are to reduce the current to the
LEDs during an exposure, to reduce the number of LEDs that are
actuated, or to reduce the frequency with which the LEDs can be
activated. An example of reducing LED activation frequency would be
to reduce the number of images that the imager can capture each
second, thereby eliminating the need to activate the LEDs as
frequently. For example, some area imagers are capable of capturing
images at up to 60 frames per second. This high frame rate can help
the reader feel more responsive to a user, but in the case of an
impending overheating condition, the frame rate might be reduced to
50, 40, or 30 frames per second, etc., as necessary, to achieve an
acceptable temperature. This would permit the LEDs to be turned off
during the time when the additional frames would otherwise be
occurring. Users might notice a small loss of responsiveness when
the number of frames is reduced, but this is preferable to failure
of the reader.
[0021] Many imaging engines also have LEDs or lasers that are used
to project a visual aiming pattern, mark, or beam of light on the
symbol so as to facilitate reading. These aiming components also
generate heat and are sensitive to overheating conditions. Thermal
management procedures could therefore include the ability to reduce
an electrical drive current to energize an aiming light source, to
reduce a frequency of activation of the aiming light source (for
example, only activating the aiming pattern every other frame), or
to entirely turn off any aiming light source when the temperature
exceeds a predetermined threshold.
[0022] When an overheating condition is detected by the thermal
sensor that requires initiation of heat reducing procedures such as
those described above, the scan engine can transmit a message, i.
e., the control signal, to the host or to the controller that
indicates that the overheating situation is occurring, so that
measures can be taken to reduce the excess heat, thereby insuring
that the scan engine can operate at maximum performance. For
example, if the host is in control of the frame rate, the
activation control of the illumination LEDs, or the aiming light
source, the host can implement thermal management procedures as
outlined above. Alternatively, or in addition, the controller, that
decodes the symbol and controls some of the other reader
components, can implement some or all of the thermal management
procedure, either independently or in combination with the host
[0023] The message sent to the host may take the form of
transmitting the control signal from the thermal sensor directly to
the host so that the host can monitor the scan engine temperature.
Alternatively, if the scan engine includes an on-board
microprocessor, then the message can be transmitted by activating a
dedicated line or by transmitting the message in digital form.
[0024] In accordance with another aspect of the invention, the
method of electro-optically reading indicia, comprising the steps
of capturing return light from the indicia during reading by using
a solid-state imager including an array of image sensors;
generating and directing high intensity illumination light from a
light source to the indicia with concomitant generation of excess
heat; and dissipating the excess heat to improve reader
performance.
[0025] In accordance with yet another aspect of the invention, an
imaging module for use in electro-optically reading indicia,
comprises a chassis; a solid-state imager supported by the chassis,
including an array of image sensors for capturing return light from
the indicia during reading; a light source supported by the
chassis, for generating and directing high intensity illumination
light to the indicia with concomitant generation of excess heat;
and means for dissipating the excess heat to improve reading
performance.
[0026] Hence, by removing the excess heat, the operating lifetimes
of the imager, the LEDs, the controller and other reader components
are extended, and the performance of the reader is enhanced.
[0027] The novel features which are considered as characteristic of
the invention are set forth in particular in the appended claims.
The invention itself, however, both as to its construction and its
method of operation, together with additional objects and
advantages thereof, will be best understood from the following
description of specific embodiments when read in connection with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a perspective view of one embodiment of an imaging
reader operative for capturing light from symbol-bearing targets in
accordance with this invention;
[0029] FIG. 2 is a perspective view of another embodiment of an
imaging reader operative for capturing light from symbol-bearing
targets in accordance with this invention;
[0030] FIG. 3 is a block diagram of various components of the
reader of FIG. 1;
[0031] FIG. 4 is a schematic view of yet another embodiment of an
imaging reader operative for capturing light from symbol-bearing
targets in accordance with this invention;
[0032] FIG. 5 is a perspective view of an imaging module for use
with any of the readers;
[0033] FIG. 6 is an enlarged, exploded, perspective view of the
imaging module of FIG. 5;
[0034] FIG. 7 is a front elevational view of a detail within the
imaging module of FIG. 5; and
[0035] FIG. 8 is a sectional view of a detail within the imaging
module of FIG. 5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] Reference numeral 10 in FIG. 1 generally identifies a
workstation for processing transactions and specifically a checkout
counter at a retail site at which products, such as a can 12 or a
box 14, each bearing a target symbol, are processed for purchase.
The counter includes a countertop 16 across which the products are
slid at a swipe speed past a generally vertical window (i.e.,
presentation area) 18 of a box-shaped, portable, vertical slot,
imaging reader 20 mounted on the countertop 16. A checkout clerk or
operator 22 is located at one side of the countertop, and the
reader 20 is located at the opposite side. A cash/credit register
24 is located within easy reach of the operator. In the frequent
event that large, heavy, or bulky products, that cannot easily be
brought to the reader 20, have target symbols that are required to
be read, then the operator 22 may also manually grasp the portable
reader 20 and lift it off, and remove it from, the countertop 16
for reading the target symbols in a hand-held mode of operation.
The reader need not be box-shaped as illustrated, but could have
virtually any housing configuration, such as a gun shape, as
depicted in FIGS. 2 and 4.
[0037] Reference numeral 30 in FIG. 2 generally identifies another
imaging reader having a different configuration from that of reader
20. Reader 30 also has a generally vertical window (i.e.,
presentation area) 26 and a gun-shaped housing 28 supported by a
base 32 for supporting the reader 30 on a countertop. The reader 30
can thus be used as a stationary workstation in which products are
slid or swiped past the generally vertical window 26, or can be
picked up off the countertop and held in the operator's hand and
used as a handheld reader in which a trigger 34 is manually
depressed to initiate reading of the symbol.
[0038] As schematically shown in FIG. 3, an imager 40 and an
imaging lens assembly 41 are mounted in an enclosure 43 in either
reader, such as the reader 20. The imager 40 is a solid-state
device, for example, a CCD or a CMOS imager and has an array of
addressable image sensors operative for capturing light through the
window 18 from a target, for example, a one- or two-dimensional
symbol, over a field of view and located in a working range of
distances between a close-in working distance (WD1) and a far-out
working distance (WD2). In a preferred embodiment, WD1 is about two
inches from the imager array 40 and generally coincides with the
window 18, and WD2 is about eight inches from the window 18. An
illuminator is also mounted in the reader and includes a light
source, e.g., a light emitting diode (LED) 42, or preferably a
plurality of LEDs 42, arranged at opposite sides of the imager 40
to uniformly illuminate the target.
[0039] As shown in FIG. 3, the imager 40 and the illuminator LEDs
42 are operatively connected to a controller or microprocessor 36
operative for controlling the operation of these components.
Preferably, the microprocessor is the same as the one used for
decoding light scattered from the indicia and for processing and
analyzing the captured target images.
[0040] In operation, the microprocessor 36 sends a command signal
to pulse the illuminator LEDs 42 for a short time period, say 500
microseconds or less, and energizes the imager 40 to collect light
from a target symbol only during said time period. A typical array
needs about 33 milliseconds to read the entire target image and
operates at a frame rate of about 30 frames per second. The array
may have on the order of one million addressable image sensors.
[0041] Reference numeral 50 in FIG. 4 generally identifies a
hand-held, gun-shaped, imaging reader for electro-optically reading
indicia, such as bar code symbol 54, or other marking, located in a
range of working distances therefrom. The reader 50 has a pistol
grip handle 51 and a manually actuatable trigger 52 which, when
depressed, actuates an imaging module or scan engine 55, as
described below, to collect return light from the indicia 54. The
reader 50 includes a housing 53 in which the scan engine 55, signal
processing circuitry including a controller 60 mounted on a printed
circuit board 64, and a battery pack 59 are accommodated. A
light-transmissive window 56 at a front of the housing enables the
return light 57 to enter the housing, and allows illumination light
58 emitted from the scan engine 55, as described below, to exit the
housing. A keyboard 61 and a display 63 may advantageously be
provided on a top wall of the housing for ready access thereto.
[0042] In use, an operator holding the handle 51 aims the housing
at the symbol and depresses the trigger 52. The scan engine emits
the illumination light 58, in the same manner as the illumination
light is emitted by the illuminator 42 in FIG. 3. The return light
57 that is scattered and reflected from the symbol 54 is optically
modified and focused by an optical focusing assembly onto an imager
in the scan engine, in the same manner as the return light is
focused by the lens 41 onto the imager 40 in FIG. 3.
[0043] The scan engine 55 thus includes at least the imager 40 and
the illuminator 42, both supported on a common chassis, as
described more fully below in connection with FIGS. 5-8. Other
components, for example, the microprocessor or controller 60 that,
in a manner similar to the controller 36 of FIG. 3, decodes a
signal generated by the imager 40 to extract the data encoded in
the symbol, can also be supported on the chassis, again as
indicated below.
[0044] As discussed above, the reading performance of each imaging
reader is highly dependent on the level of the illumination light
58 that is directed to the symbol 54. The higher the level of the
illumination light 58, the better is the reading performance.
Hence, high-powered light source(s) 42 are electrically driven by
the controller 36, 60 at relatively high electrical drive currents,
thereby projecting high intensity illumination light onto the
symbol. This, however, concomitantly undesirably generates
significant excess heat that can degrade and shorten the working
lifetime of components of the reader, especially the imager 40, the
light source(s) 42 and the controller 36, 60.
[0045] In accordance with one aspect of the invention, various
thermal management procedures are employed to dissipate the excess
heat to improve reader performance. For example, each illumination
LED 42, as best seen in FIG. 7, is surface-mounted on one of a pair
of opposite surfaces 74, 76 (see FIG. 8) of a printed circuit board
70. Thermally conductive, metallized lands 72, 78 or pads,
preferably of copper, are plated on the opposite surfaces 74, 76 of
the board. A hole or thermal via 80 extends through the opposite
surfaces 74, 76 of the board 70 and is internally plated and lined
with a thermally conductive, metallized layer 82, preferably of
copper, in thermal communication with the lands 72, 78 on the
opposite surfaces 74, 76 of the board 70. Each illumination LED 42
is in thermal communication, preferably by soldering, with one of
the lands 72 to conduct the excess heat away from the respective
LED 42 from the land 72 on one surface 74 via the plated hole 80 to
the opposite land 78 on the opposite surface 76. This thermal
management procedure is especially recommended when the board 70 is
small in area such that the lands on one surface, i.e., the front
surface 74, of the board 70 are insufficient in area to radiate the
excess heat to the environment. By also using the land 78 on the
opposite rear surface 76 to dissipate the excess heat, the total
area for radiating the excess heat to the environment is increased,
and the heat-sinking capability is enhanced.
[0046] A chassis 84 (see FIGS. 6 and 8) comprised of a thermally
conductive material, e.g., zinc, is operative for supporting at
least the imager 40 on a printed circuit board 86 and the
high-powered light source(s) 42 on the board 70 that is oriented to
be parallel to the board 86. Another top printed circuit board 88
(see FIG. 5) lies between the boards 86, 70 above the chassis 84.
All electrical connections between the components on the boards 86,
70 are made via the board 88. All of these components and boards
together constitute the imaging module or scan engine 55
[0047] The metal chassis 84 is preferably in thermal communication
with one of the lands 78 to conduct the excess heat away from each
LED 42 to the chassis 84. The opposite rear surface 76 of the board
70 is in close proximity with the thermally conductive chassis 84
of the scan engine 55. Provision is made to conduct the excess heat
from the opposite rear surface 76 of the board 70 to the chassis 84
by means of a heat conductive medium 90, such as thermal grease or
thermally conductive, silicone pads. Alternatively, the land 78 on
the opposite rear surface 76 of the board 70 can be positioned in
direct contact with the chassis 84. As a result, the entire chassis
84 now becomes part of the heat sink for the high-powered light
source(s) 42.
[0048] The metal chassis 84 can have ribs or fins to aid in
radiation of the excess heat to the ambient environment, but
sometimes the scan engine 55 is embedded in a reader in such a way
as to make radiation of the excess heat unavailable. Worse yet, the
scan engine 55 may be mounted close to a heat source that may
actually increase the temperature of the scan engine 55. In these
cases, additional measures must be taken to assure that the LEDs
42, and other electronic components in the scan engine 55, do not
overheat.
[0049] In accordance with another aspect of this invention, a
thermistor, a thermocouple, or a like thermal sensor 92 (see FIGS.
3 and 4) is located in a circumambient region of the light source
42, for monitoring the temperature of the chassis 84 and sensing
when the excess heat reaches a predetermined threshold, and for
generating a control signal when the threshold has been reached.
For example, the thermal sensor 92 can be mounted on one of the
circuit boards 70, 86, 88 close to, or in contact with, the chassis
84. Thermal grease or other thermally conductive material may be
used to insure that the thermal sensor 92 is thermally connected to
the chassis 84, the circuit board 70 that supports the LEDs 42, or
other part of the scan engine 55 that is deemed to be
representative of the temperature sensitive components in the scan
engine 55 that must be protected from overheating. The controller
36, 60 is advantageously operative for causing the excess heat to
be reduced upon generation of the control signal. Alternatively, or
in addition, a host 62 (see FIG. 4) in communication with the
reader via a radio frequency or infrared transceiver 94 is provided
for causing the excess heat to be reduced upon generation of the
control signal.
[0050] Various thermal management procedures include at least one
of the controller 36, 60 and the host 62 being operative for
shutting off the light source 42 upon generation of the control
signal; or for energizing the light source 42 for a time period
during reading with the high intensity illumination light 58, and
for shortening the time period upon generation of the control
signal; or for driving the light source 42 with a high amplitude
drive current during reading with the high intensity illumination
light 58, and for reducing the high amplitude drive current upon
generation of the control signal; or for driving the light source
42 comprised of a plurality of light emitting diodes (LEDs) during
reading with the high intensity illumination light 42, and for
reducing the number of LEDs upon generation of the control signal;
or for causing the imager 40 to capture the return light in a
plurality of images per frame during reading with the high
intensity illumination light 58, and for reducing the number of
images captured per frame upon generation of the control signal; or
for periodically energizing the light source 42 to cause the high
level illumination light 58 to illuminate the indicia 24 during a
plurality of frames, and periodically deenergizing the light source
42 to cause the high level illumination light 58 not to illuminate
the indicia during at least one of the frames upon generation of
the control signal. All of these thermal management procedures have
in common the feature of reducing the heat generated by the LEDs
42. The thermal management procedures may be initiated in
succession or in combinations depending on how hot the scan engine
55 gets. At a first temperature threshold, moderate thermal
management procedures can be initiated. If temperature continues to
rise, further more aggressive thermal management procedures can be
initiated.
[0051] One possible thermal management procedure could be to
inhibit activation of the LEDs 42 and other components of the scan
engine 55 entirely until such time as the temperature returns to an
acceptable threshold level. Another possibility is to reduce the
time that the LEDs 42 are permitted to be turned on for each
exposure of the imager. Other possibilities are to reduce the
current to the LEDs 42 during an exposure, to reduce the number of
LEDs 42 that are actuated, or to reduce the frequency with which
the LEDs 42 can be activated. An example of reducing LED activation
frequency would be to reduce the number of images that the imager
40 can capture each second, thereby eliminating the need to
activate the LEDs 42 as frequently. For example, some area imagers
40 are capable of capturing images at up to 60 frames per second.
This high frame rate can help the reader feel more responsive to a
user, but in the case of an impending overheating condition, the
frame rate might be reduced to 50, 40, or 30 frames per second,
etc., as necessary, to achieve an acceptable temperature. This
would permit the LEDs 42 to be turned off during the time when the
additional frames would otherwise be occurring. Users might notice
a small loss of responsiveness when the number of frames is
reduced, but this is preferable to failure of the reader.
[0052] Many imaging engines 55 also have an aiming light source 96
(see FIG. 6), such as an LED or laser that is used to project a
visual aiming pattern, mark, or beam of light on the symbol 54 so
as to facilitate reading. The aiming light source 96 is mounted on
the board 86 and also generates heat and is sensitive to
overheating conditions. A support plate 98 supports lenses or
optical elements 100, such as a diffractive element or a Fresnel
lens, to optically modify the aiming beam generated by the aiming
light source 96 to create the aiming pattern. One or more of the
lenses 100 could also be used to focus the illumination light 58.
The focusing lens assembly 41 for focusing the return light 57 onto
the imager 40 extends through the support plate 98. Thermal
management procedures could therefore include the ability to reduce
an electrical drive current to energize the aiming light source 96,
to reduce a frequency of activation of the aiming light source 96
(for example, only activating the aiming pattern every other
frame), or to entirely turn off any aiming light source 96 when the
temperature exceeds a predetermined threshold.
[0053] When an overheating condition is detected by the thermal
sensor 92 that requires initiation of heat reducing procedures such
as those described above, the scan engine 55 can transmit a
message, i. e., the control signal, to the host 62 or to the
controller 36, 60 that indicates that the overheating situation is
occurring, so that measures can be taken to reduce the excess heat,
thereby insuring that the scan engine 55 can operate at maximum
performance. For example, if the host 62 is in control of the frame
rate, the activation control of the illumination LEDs 42, or the
aiming light source 96, the host 62 can implement thermal
management procedures as outlined above. Alternatively, or in
addition, the controller 36, 60, that decodes the symbol 54 and
controls some of the other reader components, can implement some or
all of the thermal management procedure, either independently or in
combination with the host 62
[0054] The message sent to the host 62 may take the form of
transmitting the control signal from the thermal sensor 92 directly
to the host 62 so that the host 62 can monitor the scan engine
temperature. Alternatively, if the scan engine 55 includes an
on-board microprocessor, the message can be transmitted by
activating a dedicated line or transmitting the message in digital
form.
[0055] In accordance with another aspect of the invention, the
method of electro-optically reading indicia, comprising the steps
of capturing return light 57 from the indicia 24 during reading by
using a solid-state imager 40 including an array of image sensors;
generating and directing high intensity illumination light 58 from
a light source 42, 96 to the indicia 24 with concomitant generation
of excess heat; and dissipating the excess heat to improve reader
performance.
[0056] In accordance with yet another aspect of the invention, an
imaging module 55 for use in electro-optically reading indicia 24,
comprises a chassis 84; a solid-state imager 40 supported by the
chassis 84, including an array of image sensors for capturing
return light 57 from the indicia 24 during reading; a light source
42, 96 supported by the chassis 84, for generating and directing
high intensity illumination light 58 to the indicia with
concomitant generation of excess heat; and means for dissipating
the excess heat to improve reading performance.
[0057] Hence, by removing the excess heat, the operating lifetimes
of the imager 40, the LEDs 42, 96, the controller 36, 60 and other
reader components are extended, and the performance of the reader
is enhanced.
[0058] It will be understood that each of the elements described
above, or two or more together, also may find a useful application
in other types of constructions differing from the types described
above. Thus, readers having different configurations can be
used.
[0059] While the invention has been illustrated and described as
controlling excess heat in an imaging reader, module and method, it
is not intended to be limited to the details shown, since various
modifications and structural changes may be made without departing
in any way from the spirit of the present invention.
[0060] Without further analysis, the foregoing will so fully reveal
the gist of the present invention that others can, by applying
current knowledge, readily adapt it for various applications
without omitting features that, from the standpoint of prior art,
fairly constitute essential characteristics of the generic or
specific aspects of this invention and, therefore, such adaptations
should and are intended to be comprehended within the meaning and
range of equivalence of the following claims.
[0061] What is claimed as new and desired to be protected by
Letters Patent is set forth in the appended claims.
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